The present invention relates generally to the control of emergency lighting units for providing secondary lighting in selected areas when primary lighting systems fail due either to a voltage drop in the power supply for the primary lighting system or when the primary lighting system is otherwise disabled. Specifically, this invention relates to the control of emergency lighting units which include a rechargeable battery, a battery charger powered by the primary power system and a switching element for turning on the emergency lighting element when the voltage of the primary power system falls below some predetermined threshld value. More particularly, the invention relates to the control and use of such emergency lighting units to test the unit and exercise its battery.
Emergency lighting systems for providing critical lighting needs during a failure of a primary lighting systems due to power loss are commonly found in many commercial and public buildings. These systems are used not only to alleviate panic and anxiety of occupants during power outage in buildings wtih very few or no windows but also to illuminate poorly lighted interior corridors and stairwells of buildings that are otherwise open to light that may be critical paths of exit during emergencies involving power failures and in areas which might provide critical routes of escape at night. Light provided by these units may also facilitate life saving and damage mitigation activities when power outages are associated with circumstances such as fires and natural disasters. Such units are often required by zoning laws and the like.
Emergency lighting units are commonly found mounted high up on walls in theatres, retail buildings, warehouses, and corridors of public buildings. They most commonly consist of one or more lighting elements mounted on a cabinet which houses a rechargeable power source, for example, a rechargeable battery, a charging unit to recharge the power source and a switching device for switching on the emergency lighting system when the voltage of the power source for the primary lighting system falls below a predetermined voltage. These units generally draw power for recharging the batteries from the primary power source. During periods over which the emergency units are not needed, the battery charger typically maintains a constant voltage trickle charge on the rechargeable battery to insure it is maintained at full capacity to be available when needed in an emergency situation. The switching unit is also connected to the primary power source and, when the switching unit senses the voltage of the primary source fall below a preset threshold voltage, it connects the lighting elements of the emergency system to the rechargeable power source to provide light while the primary lighting system is in a brown out or power out condition. Once the primary power source returns to a voltage level above the threshold level, the switching unit disconnects the lighting elements from the rechargeable power source and the charger unit provides a high current charge to the batteries to restore them to a fully charged condition. After the batteries have returned to float voltage, the charger again provides a constant voltage trickle charge to the batteries to maintain them in a fully charged condition for use should an emergency situation arise.
The manner in which a common state of the art emergency lighting unit functions may be readily understood with reference to the schematic illustration of FIG. 1, which shows an emergency lighting unit in its usual condition when primary line voltage is above the threshold value. The emergency lighting unit 1 includes lighting element 2 and battery charger 4, each included in a circuit with a rechargeable battery 3. An emergency lighting control switch 5 maintains the circuit including lighting element 2 in an open condition , as shown, so long as the primary power source voltage is above the threshold value. In this condition the battery charger 4 will provide a constant voltage trickle charge to maintain the battery 3 at full capacity. Both the control switch 5 and the charger 4 are connected to and draw their power from the primary power source 10. Should the voltage of the primary source 10 fall below the predetermined threshold voltage, emergency lighting control switch 5 will close the circuit including illuminating element 2 and battery 3 and lighting element 2 will provide emergency light drawing upon the rechargeable power source 3 until the primary power source voltage increases above the threshold value and control switch 5 reopens the illuminating element circuit of the emergency lighting unit. At that time the charger 4 will automatically provide a high current charge until the rechargeable battery 3 is fully charged at which time the charger 4 will again provide a constant voltage trickle charge to maintain the battery 3 at full capacity.
Emergency lighting systems should be subject to regular periodic inspections to insure they will be available should an emergency arise. Manufactures of these units suggest they be subject to periodic inspection, for example, every 30 days, in order to insure their proper function during emergencies. However, as in the case of many systems which are critical to the saving of lives during emergencies, when these emergency lighting units are not needed they are inconspicuous and attract little notice. Thus, inspections may be inadvertently omitted. Proper inspection of the lighting units should include checking the function of the lighting elements, rechargeable power source, charger and switching system. However, as the units are generally located in elevated positions to service to provide effective area lighting over a large illumination area and to present minimum obstruction to normal activities within the protected building, proper performance of inspections on a periodic basis frequently requires the use of ladders or lift-devices and is often difficult and time consuming and maybe performed in a cursory manner or skipped completely by maintenance personnel. Further, when inspections are time consuming and expensive, there is a natural tendency for management to divert resources to more visible and profitable activities.
Manufacturers of emergency lighting units are aware of these problems and in some cases have provided units which automatically check themselves on a periodic basis, for example, every 30 days. The unit may include a device which simulates a power outage for a brief period of time during which battery voltage and lamp operation are internally checked and a visual or audio alarm triggered if the unit is in need of servicing. Frequently, however, these alarms are provided with an override button by which the alarm may be reset so that it will not be activated again until the next automatic periodic test is initiated, thus providing a "quick fix" for maintenance personnel.
Rechargeable battery power sources such as utilized in many of these emergency units loose their ability to store electrical power over time. Generally, their power-storage ability will deteriorate more quickly if they are constantly kept in a fully charged state rather than allowed to fully or partially discharge from time to time. In most emergency lighting installations, periodic manual testing by service personnel, or automatic self-testing of the unit, do not exercise the rechargeable batteries sufficiently to significantly extend their service life. Further, the test operation of the emergency units during working hours, while the primary lighting system is on, or on a timed basis at other times when a lighting system is not needed, is a waste of electrical energy.